We are studying the expression of receptors for cytokines during the process of differentiation of myeloid cells to mature macrophages. Recent studies show that activated monocytes and macrophages, in addition to T and B cells, also express receptors for IL2 (IL2R). We have shown that, during the process of differentiation of myeloid cells to mature macrophages, the cells express the low affinity receptor for IL2 (IL2R`). IL1 is known to enhance the expression of IL2R` on T cells. Thus, in the present study, we tested whether IL1 will have a similar effect on the expression of the IL2Ralpha in differentiating myeloid cells. The murine myeloid leukemia M1 cell line stimulated with IL6 is used as a model for myeloid differentiation. By cytofluorometry, utilizing monoclonal antibodies against the IL2Ralpha, we found that the expression of IL2R` induced by an optimal concentration of IL6 is further enhanced by IL1. Binding data with 125I-IL2 and Scatchard analysis confirmed these results and in addition showed an increase in low affinity binding sites for IL2 from 3100/cell in cells stimulated with IL6 to 17620/cell in cells stimulated with IL6+IL1. Affinity crosslinking of 125-IL2 to M1 cells stimulated with IL6 or with IL6+IL1 detected only a receptor complex of about 55kDa, which fits the MW of IL2Ralpha. Northern analysis revealed an increase in the steady state levels of mRNA for the IL2Ralpha but not for the IL2Rbeta in cells stimulated with IL6+IL1. Nuclear run-on analysis and actinomycin D chase experiments showed that this change in mRNA is due to an increase in the transcription rate of the IL2Ralpha gene induced by IL1 rather than by an increase in stabilization of the IL2Ralpha mRNA. We also studied the expression of cell bound and soluble receptors for IL4 during myeloid differentiation after induction of M1 cells with IL6. These experiments were done in collaboration with Drs.Feldman and Finbloom (DCB, CBER). Results of these experiments are presented in Dr. Gerald Feldman's annual report.